The occurrence of volatile odorous substances is one of the problems associated with the collection and treatment of various waste materials. Domestic sewage is the largest volume source of odorous waste for which sulfides and thiols are very common odor causing constituents. Sulfides are most prominent, with hydrogen sulfide being the most objectionable odor-bearing compound in such wastes. Because of the magnitude of domestic sewage that is collected and treated and the prominence of odorous sulfidic compounds associated with this waste, the present invention is particularly directed, but not limited to the control of hydrogen sulfide and other sulfide odors in sewage. As used herein, the term "hydrogen sulfide" (H.sub.2 S) also includes other sulfides of divalent sulfur.
Biological activity, especially anaerobic decomposition of compounds containing sulfur, is responsible for the formation of most odorous sulfur compounds, especially H.sub.2 S. Sulfate ion (SO.sub.4.sup.-2) is the most common starting material for the generation of H.sub.2 S. In the absence of oxygen, sulfate-reducing bacteria (for example, desulfovibrio desulfuricans) will metabolize sulfate ion together with organic matter present to form H.sub.2 S, as represented by the following equation: EQU SO.sub.4.sup.-2 +organic matter+bacteria.fwdarw.H.sub.2 S+CO.sub.2 +H.sub.2 O
The odor associated with H.sub.2 S is similar to rotten egg odor. H.sub.2 S is toxic in low concentrations. Hydrogen sulfide is also corrosive towards steel and concrete. The presence of H.sub.2 S and other odor causing compounds in waste materials is a major concern for waste handling systems. One aspect of the occurrence of malodorous compounds that is often the driving force behind efforts to control odor is complaints received from citizens living in the area. Such odors are generally regarded as a public nuisance and a health hazard.
Hypochlorite (sodium or calcium), potassium permanganate, sodium nitrate, ferrous and ferric chloride, ferrous sulfate, hydrogen peroxide, chlorine, chlorine dioxide, and sodium chlorite have been widely used for the control of odor in wastes, and sewage waste in particular. For example, articles have been published and patents have been granted for the use of sodium chlorite and sodium nitrate individually to control odorous compounds. The following references mention the use of sodium chlorite by itself for odor control:
"Control of Odors from Sewage Sludge," Gas, Wasser, Abwasser, Vol. 65, pp. 410-413 (1985) in Chemical Abstracts 104:10062 (German); PA0 "Polyelectrolyte Conditioning of Sheffield Sewage Sludge," Water Science Technology, Vol. 16, pp. 473-486 (1984) in Chemical Abstracts 102:100249; PA0 "Slime and Odor Elimination in Process Water of the Paper Industry," Papier, Vol. 29, pp. 43-51 (1975) in Chemical Abstracts 85:82749 (German); and PA0 "Deodorization of Sludge for Dewatering by Controlled Adding Chlorite," Japanese Patent Publ. No. 06320195 (1994). PA0 "Method of Sewage Treatment," U.S. Pat. No. 5,114,587 (May 9, 1992); PA0 "Process for Removal of Dissolved Hydrogen Sulfide and Reduction of Sewage BOD in Sewer or Other Waste Systems," U.S. Pat. No. 4,911,843 (Mar. 27, 1990); and PA0 "Use of Alkali Metal Nitrites to Inhibit H.sub.2 S Formation in Flue Gas Desulfurization System Sludges," U.S. Pat. No. 4,681,687 (Jul. 21, 1987).
The following patents mention the use of nitrate by itself for odor control:
In addition, patents have been issued for the use of oxidants in combination with nitrates. For example, U.S. Pat. No. 4,108,771 contains claims directed to the use of sodium chlorate and ammonium nitrate for odor control of waste materials. U.S. Pat. No. 3,966,450 contains claims directed to the use of hydrogen peroxide and the addition of nitric acid to generate nitrate salts. U.S. Pat. No. 5,200,092 contains claims directed to the use of potassium permanganate with nitrate salts for odor control.
Some of the treatments mentioned above have advantages in certain applications. However, they also suffer from various drawbacks. Some of the disadvantages of the above-mentioned treatment chemicals are listed below.
______________________________________ Hypochlorite/chlorine Loses strength during storage. Reacts with ammonia for additional consumption. Forms chlorinated VOCs. Generates chlorine odor with over-doses. Has no long-term effect. Potassium Permanganate Is labor intensive. Causes discoloration with over-doses. Results in precipitation of manganese. Nitrates Have no immediate or short term effect. Produce nitrogen by-products which can present treatment problems. Iron Salts Are ineffective for non-sulfide odors. Cause build-up of solids. Impure products can contain heavy metals. Can be toxic to microorganisms. Deplete dissolved oxygen and alkalinity. Hydrogen Peroxide Requires catalysis for non-sulfide odors. Causes foaming. Is not long lasting. Chlorine Dioxide Requires a generator. Generates chlorine-type odor with over-doses. Is not long lasting. Sodium Chlorite Can be costly in high doses. ______________________________________
In view of the disadvantages mentioned above, there is a need in the art for a method and composition for abating odor in waste materials that is cost effective and that not only works well on all malodorous compounds, but that does not produce undesirable by-products. Accordingly, it is an object of the present invention to address this need in the art. This and other objects of the present invention will become more apparent in light of the following summary and detailed description of the invention and the appended claims.